Elastomer-free fabric surface for power transmission belt tooth facing

ABSTRACT

An endless positive drive belt is described having a tensileloaded castable elastomeric body supporting circumferentially spaced cogs or teeth. The alternating land and teeth portions of the belt carry a layer of wear-resistant fabric, the outer surface of which is free of elastomer due to the presence of a bonded layer of elastomer impervious material. A method for producing the belt is described.

United States Patent [191 Redmond, Jr.

ELASTOMER-FREE FABRIC SURFACE FOR POWER TRANSMISSION BELT TOOTH FACINGInventor: John D. Redmond, Jr., Denver,

Colo.

The Gates Rubber Company, Denver, Colo.

Filed: Sept. 7, 1973 Appl. No.: 395,084

Assignee:

US. Cl. 156/138; 156/245; 264/263; 428/169; 428/339; 428/172; 428/179;428/224; 428/425 Int. Cl. 829" 7/22; B29H 3/00 Field of Search 156/137,138, 139, 140, 156/141; 264/263 References Cited UNITED STATES PATENTS6/1964 Haines et a1 156/138 1 July 15, 1975 3,200,180 10/1965 Russ eta1. 264/271 3,580.767 5/1971 Barnes et a1. 156/138 3,607,502 9/1971Marzocchi et a1. 156/137 3,673,883 7/1972 Adams 156/138 PrimaryExaminerGeorge F. Lesmes Assistant Examiner-William R. Dixon, Jr.Attorney, Agent, or Firm-Curtis H. Castleman, Jr.; Raymond Fink; H. W.Oberg, Jr.

[5 7] ABSTRACT An endless positive drive belt is described having atensile-loaded castable elastomeric body supporting circumferentiallyspaced cogs 0r teeth. The alternating land and teeth portions of thebelt carry a layer of wear-resistant fabric, the outer surface of whichis free of elastomer due to the presence of a bonded layer of elastomerimpervious material. A method for producing the belt is described.

18 Claims, 4 Drawing Figures ELASTOMER-FREE FABRIC SURFACE FOR POWERTRANSMISSION BELT TOOTH FACING BACKGROUND OF THE INVENTION Thisinvention relates to endless belts of the cog type containing a shear,abrasion and noise resistant inner cover element which is substantiallyfree of elastomer at its surface, and further relates to a method forproducing such belts. This invention relates to and defines animprovement over my co-pending application Ser. No. 189,440, filed Oct.14, l97l, now US. Pat. No. 3,772,929, and assigned to the assignee ofthe subject invention and hereby incorporated by reference.

It has been recognized that power transmission belts constructed of acastable elastomer, e.g. liquid polyurethane, offer a number ofsignificant advantages over conventional rubber belting. Among theseadvantages are that the liquid cast belt is less susceptible to flexfatigue, it can be driven around smaller sheaves, and demonstratesimproved load life. These cast belts may be vacuum spin cast in a singleoperation as contrasted to the numerous steps required to buildconventional rubber tooth-type belts. However, many of the castabletiming belts, and particularly those constructed of urethane, are oftennoiser and run hotter than a comparable rubber belt due primarily to thedifference in coefficient of friction of the material. The urethane beltis generally more aggressive as it enters and leaves the sprocket orsheave and builds up considerable heat at the interfaces. This heatbuild-up reduces the efficiency of the belt and the higher operatingtemperatures can reduce belt life considerably by lowering the tearstrength of the cog, or by attacking the bond between the elastomer bodyand tensile cord embedded therein.

One solution to the noise and heat-build-up problem is to reduce thecoefficient of friction of the sheaveengaging surface of the belt byisolating or removing as much elastomer from mear the surfaces of thebelt which come into contact with the sprocket teeth or flanges. Thisapproach was taken in my abovementioned co-pending application in whichI was able to isolate a large portion of the elastomer from thesheave-engaging surfaces of the belt by incorporating a wear-resistantfabric layer along the surface of the belt together with theincorporation of cross cords in the body of the cogs, thus eliminatingmuch of the elastomer in the critical areas. However, as acknowledged inmy co-pending application, there was still present an outer skim coatingof elastomer on the surface of the belt. This outer layer, even thoughrelatively thin, eg about 2 mils in thickness, exhibits high abrasionand wear-resistance and by virtue of its high coefficient of frictioncauses significant increases in heating and noise level of the belt,particularly for heavy duty applications.

It is a primary object of the invention to provide a belt constructionand method therefor which overcome drawbacks of prior constructions andin which the castable elastomer is isolated from the outer surface ofthe wear-resistant fabric layer positioned along the sheaveengagingsurface of the belt.

SUMMARY OF THE INVENTION Briefly described, the objects of the inventionare met by the provision of an endless positive drive power transmissionbelt including a tensile-loaded body portion composed of a liquid castelastomeric material, a

plurality of spaced teeth bonded with and disposed along the innerperiphery of the body portion, a layer of wear-resistant fabricpositioned substantially along the periphery of the alternating land andteeth portions of the belt, and a layer of elastomer impervious materialbonded so it preferably adheres to only a portion of the total thicknessof the weanresistant fabric and positioned along the outer,sheave-engaging face of the land and teeth portions of the belt.

According to the method, the above-described power transmission belt isproduced by the steps comprising 1) bonding the elastomer imperviousmaterial to preferably only one side of the wear-resistant fabric layer,2) forming a mold cavity defined by a mold mandrel and an outer shell,one of the mandrel or shell having a plurality of notches correspondingto the shape of the teeth or cogs, 3) wrapping the bonded wear-resistantfabric about the surface of the notched mold portion in a manner suchthat the layer of elastomer impervious material is adjacent the notchedmold portion, 4) applying a tensile layer about the wear-resistantfabric, and 5) introducing a substantially liquid elastomeric materialinto the mold cavity and polymerizing the thus formed product.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred aspects of this inventionwill be described with reference to the accompanying drawings, in whichlike numerals designate like parts in the several figures, and wherein:

FIG. I is a fragmentary, perspective view of a power transmission beltmade according to the invention;

FIG. 2 is a longitudinal cross-sectional fragmentary view ofahigh-torque timing belt made according to the invention;

FIG. 3 depicts mold apparatus for manufacturing the belts according tothe invention; and

FIG. 4 is a schematic, blown up view of the bonded wear-resistant fabriclayer utilized in the construction of the belt.

PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIG. I, an endlesscog-type power transmission belt is generally shown at 10. The beltincludes a body having an overcord section 12 ofa castable elastomericmaterial and a series of spaced cogs or teeth 16, also containing anelastomeric material 14. The elastomeric material utilized in theovercord and tooth body are compatible and may be of the same ordifferent type elastomer. The elastomer overcord section 12 ispreferably loaded with a reinforcing tensile layer or plurality oftensile members such as the longitudinally extending and spaced tensilecords 18. These tensile members may consist of one or more strands of aconventional stress-resistant material such as polyamide cord, fiberglass, polyester cord or wire filaments. The tensile members may bepre-stressed or impregnated with a suitable material if desired.

Various types of elastomeric materials are available which may be castand which would be suitable according to the subject invention. Examplesare curable liquid elastomers exemplified by plastisols, organosols,liquid chloroprenes, liquid polysulfides, liquid rubbers, silicones,epoxides, urethanes, carboxylated butadieneacrylonitrile, polyesterbased resins, polyether based resins, and the like. Polyurethaneelastomers are generally preferred at present because of their tensilestrength, abrasion resistance and satisfactory modulus and elasticity.The polyurethanes may be prepared in conventional manner, such as bycompounding a urethane prepolymer (formed by reaction of an activehydrogen-containing compound with a polyisocyanate) with a curing agentand an amount of plasticizer or other ingredient, if desired.Conventional curing agents may be utilized, such asorganohydrogen-containing compounds exemplified by substituted aromaticamines.

Reinforcing fabric 22 intimately fits along the alternating teeth 16 andalternating land portions 24 of the belt to form a face cover therefor.This fabric may be of any desired configuration such as a conventionalweave consisting of warp and weft threads at any desired angle, or mayconsist of warp threads held together by spaced pick cords, of a knittedor braided configuration, and the like. More than one ply of fabric maybe employed. If desired, the fabric may be cut on a bias so that thestrands form an angle with the direction of travel of the belt.Conventional fabrics may be employed using such materials as cotton,polyester, polyamide, hemp, jute, fiber glass and various other naturaland synthetic fibers. In a preferred embodiment of the invention, thefabric layer 22 consists of an expansible wear-resistant fabric in whichat least one of the warp or weft threads is made of nylon.

According to the invention, the wear-resistant fabric layer 22 carriesan adherent layer of elastomer impervious material 20 bonded so itadheres to only a portion of the total thickness of the wear-resistantfabric and positioned along the outer, sheave-engaging face of the teethand land portions of the belt. By elastomer impervious material is meanta material which adheres to one side of the wear-resistant fabric layer22 so that during the casting operation the elastomer imperviousmaterial seals the outer side only of the fabric and thereby isolatesthe elastomer from the outer surface of the fabric layer by preventingthe fibers on the outermost surface of the fabric layer from becomingcompletely encapsulated by elastomer; in this manner, the outer portionof the sheave-engaging surface of the fabric layer is substantially freeof elastomer. This feature is illustrated in FIG. 4 of the drawings.Referring to that Figure, elastomer impervious material 20 is bonded toa portion of the outer surface of wear-resistant fabric layer 22consisting in this case of a plurality of warp threads 26 and aplurality of weft or fill threads 28 (only one of which is shown). Inthis embodiment the sealing material 20 is bonded to the fill strand orfiber 28 between points a and b, c and d, which generate in threedimensions a pair of tangential contact zones or surfaces which mightresemble the shape of a contact lens or an arch, for instance. Whilesome of the elasto mer may penetrate the volume 27 bounded by theclastomer impervious layer 20 and the surrounding warp threads 26 andweft threads 28, such penetration will not extend to the surface of thefabric layer which essentially alone engages the sheaves duringoperation.

It is critical to the invention that the elastomer impervious material20 seal the outermost surface of the fabric layer so as to prevent theintrusion of elastomer into that area, and also of equal importance inthe preferred embodiment that the innerside of the fabric layer be freefrom encroachment by the elastomer impervious material so that suchinnerside of the fabric may adequately adhere to the elastomer in thebody of the belt and thus prevent the fabric from being stripped off thebelt teeth during service. In this regard, while it is only necessarythat the outer surface of the fabric layer be sealed and the innermostsurface have sufficient free area for bonding with the elastomer body ofthe belt, it is preferred that the depth of penetration into the fabriclayer of the elastomer impervious material be no more than about andmore preferably no more than about 20%, and most preferably in the rangeof 48%. However, in the event the elastomer impervious material also iscapable of forming a strong bond with the elastomer, the depth ofpenetration may be percent.

The elastomer impervious material may be made from various types ofmaterials and may be applied in a number of different ways according tothe particular desired end use envisioned. In a preferred embodiment theelastomer impervious material consists of a polymeric sheet ofthermoplastic material, for instance, which has been bonded to thewearresistant fabric by a conventional heat bonding technique utilizingelevated temperature and pressure. Polyethylene sheeting of 1-2 mils inthickness has been found satisfactory for this purpose; the bondingtemperature may be 230250F and the pressure varied so that upon castingthe elastomer is unable to penetrate and encapsulate the outer fibers ofthe fabric. A double platen press may be used in this regard. Variousother types of sheeting material, such as contact paper and films ormembranes of copolymeric synthetic materials and various naturalmaterials such as cellulosic materials are useful. The invention alsocontemplates the alternative treatment of the wear-resistant fabriclayer by such means as calendaring, brushing, dipping or sprayingpreferably on one side only of the fabric with a suitable sealant. Forinstance, a paste or resinous layer of a polymeric material dispersed ordissolved in a suitable carrier or solvent can be applied to one surfaceof the fabric. Latex and silicone are examples of useful materials.Similarly, the fabric surface can be treated by applying a layer ofpolytetrafluoroethylene. In any event, the bond between the elastomerimpervious material and wear-resistant fabric may be mechanical,chemical, electrostatic, etc.

It is contemplated in a preferred embodiment of the invention that theelastomer impervious material may suitably have very poor abrasionresistance so that upon use of the belting material the layer ofmaterial will partially or fully wear off, leaving an outer,elastomer-free surface of the wear-resistant fabric for engagement withthe rotating sheave. Polyethylene sheeting will readily wear off in thismanner. Inasmuch as the elastomer body of the belt has been fully cured,there will be no tendency for it to bleed or permeate through theinterstices in the outer fabric layer during use which would otherwisepresent the undesirable contact of the elastomer with the sheave.

Alternatively, the elastomer impervious material may be made of amaterial which has good abrasion resistance and which will thereforeremain on the inner surface of the cogs and land portion of the beltthroughout at least a significant portion of its life. In this case, thepolymer impervious material must have a coefficient of friction which issignificantly lower than the coefficient of friction of the elastomerutilized to thereby lower heat build-up, reduce noise and improve theoverall efficiency of the belt.

An alternative belt configuration is shown in FIG. 2 which, unlike thestandard pitch-type shown in FIG. 1, is designed for high-torquecapability. This belt, with the exception of the peripheral elastomerimpervious layer is described in my aforementioned co-pendingapplication. This belt consists of the usual elastomeric overcordsection 32 containing a circumferentially extending tensile cords orlayer 34. The undercord of the belt carries a plurality of spaced teethor cogs 36 which have an outer wear and abrasion resistant fabric 22 towhich is bonded elastomer impervious layer 20. A plurality of transversemembers 30 fill a major proportion of the cogs 36 and particularly fillthe vertical distance between the tensile member 34 and the addendum ofthe cogs. Both the transverse members 30 and wearresistant fabric cover22 combine to minimize the amount of elastomer in the area of the cogs.Furthermore, according to the invention the elastomer impervious layer20 substantially isolates the elastomer from the sheave-engaging surfaceof the belt.

A polyurethane belt essentially identical to the construction shown inFIG. 2 was tested and found to operate at a temperature in the range ofl60-l80F. The identical belt without the elastomer impervious layer 20and with a skim layer of polyurethane was operated under the sameconditions and found to generate temperatures in the range of 200-240F.Belts of the construction of the subject invention have averaged about35F. lower in running temperature than the same belt without the(initial) elastomer impervious layer. Load life tests have shown thatthe life of all types of V-belts generally doubles for every 18F. cooleroperating temperature increment. (See Lundstrom and Schock, MachineDesign, Dec. 9, 1971, pp 129-130). The cooler running temperature of thetiming belt of the subject invention is mostly attributable to theisolation of the elastomer from the surface.

An apparatus suitable for casting either of the cog belts of FIG. 1 orFIG. 2 is shown in FIG. 3. A preferred general technique for producingbelts according to the invention is described particularly in myaforementioned co-pending application, in U.S. Pat. No. 3,138,962(Haines et al) and U.S. Pat. No. 3,200,180 (Russ et al). As shown inFIG. 3, a casting assembly 33 broadly comprises an outer vacuum chamber35, a platform 37 upon which the vacuum chamber rests, a centralrotatable shaft 38 extending from the outside of the vacuum chamberthrough the platform into the chamber upon which is supported aninterior mandrel 40, and an outer-spaced concentric mold shell 42. Thevacuum chamber may be evacuated by an exhaust line 44, which isconnected to a vacuum pump (not shown). Liquid casting material isintroduced by means of an entry port 46 which is directed toward the topof a distributing plate 48. As the assembly is rotated, the liquidelastomer is forced to the outer regions by means of centrifugal forceand by means of a baffle system and guide system incorporated as part ofthe distributing plate 48. On the outer region of the plate, the liquidis then directed to annular cavity 41 between the central mandrel 40 andthe outer mold shell 42.

The details of the mandrel and outer mold shell configuration are setforth in my aforementioned copending application. Normally, the mandrel40 will have spaced axially extending notches and alternating upstandingportions which correspond to the cogs and land portions of the belt,respectively.

In the method of the invention, the elastomer impervious material isfirst bonded or otherwise adhered to one side only of the wear-resistantfabric resulting in a configuration exemplified in FIG. 4. The bondedwearresistant fabric may then be wrapped around the surface of thenotched mold portion (e.g. mandrel) in a manner such that the layer ofelastomer impervious material is adjacent the notched mold portion. Thewear-resistant layer may be made to conform to the notched mold portionby weaving in the notches the cross cord members, as described in theaforementioned co-pending application. The next step involves applying atensile layer, such as by helically winding tensile cord around thecircumference of the notched mandrel on top of the wear-resistant fabriclayer, forcing the bonded fabric to essentially conform to the surfaceof the notches. Finally, a substantially liquid elastomeric material isintroduced into the mold cavity and the material is polymerized to formthe desired belt configuration. Centrifugal casting combined withapplied vacuum may be employed for good results.

After polymerization has taken place and sufficient cure time allowed,the mold may be disassembled and the resultant sleeve of belts cut intoindividual belts of desired width. A skiving operation may be employedto give the desired final configuration to the teeth and/or the overcordside of the belt. In this latter regard, the overcord of the belt maycarry multiple Vs, cogs, or other configurations as desired.

It should be understood that the invention is capable or a variety ofmodifications and variations which will become apparent to those skilledin the art upon a reading of this specification. Such modifications andvariations and equivalents are intended to be a part of the scope of theinvention as defined by the appended claims.

What is claimed is:

1. In a method for producing a positive drive castable elastomeric powertransmission belt having a plurality of spaced cogs attached to a bodysection including a tensile section, said cogs having positionedapproximately along their surface a layer of wear-resistant fabric, theimprovement comprising isolating the cast elastomer from the outersurface of the fabric layer by the steps of:

adhering to one side of the wear-resistant fabric a layer of elastomerimpervious material which has been cured or set, the layer of elastomerimpervious material penetrating into and sealing said outer surface ofthe fabric layer, said elastomer impervious material being a material ofthe same type or different type from the cast elastomer;

forming a mold cavity defined by a mold mandrel and an outer shell, oneof said mandrel or shell having a plurality of notches corresponding tothe shape of the cog; wrapping the bonded wear-resistant fabric aboutthe surface of the notched mold portion in a manner such that the layerof elastomer impervious material is adjacent the notched mold portion;

applying a tensile layer about the wear-resistant fabdo, and

introducing a substantially liquid elastomeric material into the moldcavity and polemerizing the thus formed product, whereby the liquidelastomeric material does not penetrate the outer surface of the fabriclayer.

2. The method of claim 1 wherein the elastomer impervious materialconsists of a thin polymeric sheet.

3. The method of claim 2 wherein polyethylene sheet is heat bonded toone side only of the wear-resistant fabric at a temperature and pressureso that the polyethylene penetrates through the surface on the bondingside of the wear-resistant fabric, but does not penetrate the oppositesurface of the wear-resistant fabric.

4. The method of claim 3 wherein the temperature is maintained in therange from about 230 to about 250F.

5. The method of claim 1 wherein the layer of elastomer imperviousmaterial is brought adjacent the notched mold portion by the use offibrous cross cords which are wound about the notches of the mandrel andwhich are forced against the wear-resistant fabric by winding thetensile layer on top of such fibrous cross cords urging thewear-resistant fabric into the notches.

6. The method of claim 1 wherein the elastomer impervious material haspoor abrasion resistance whereupon rotation of the belt about acooperating sheave will cause the elastomer impervious material to atleast partially wear off.

7. The method of claim 1 wherein the layer of elastomer imperviousmaterial forms a strong bond with the cast elastomer and further whereinthe depth of penetration of the elastomer impervious material into thewear-resistant fabric layer is substantially 100 percent.

8. A method for the production of positive drive liquid castableelastomeric power transmission belts including a plurality of teethloaded with the cast elastomer and disposed along the driving surface ofthe belt, the teeth carrying on their outer surface a wearresistantfabric layer the outermost driving surface portion of which issubstantially free of said cast elastomer, comprising the steps of:

attaching to at least one side of the wear-resistant fabric a layer ofmaterial impervious to the liquid castable elastomer, the layer ofimpervious material penetrating into and sealing said outermost surfaceof the fabric layer;

forming a mold cavity between a mandrel and an outer shell, one of saidmandrel or shell having a plurality of notches;

disposing the wear-resistant fabric with the attached elastomerimpervious material within the cavity in a manner such that the layer ofelastomer impervious material is adjacent the notches, the side of thewear-resistant fabric opposite the side adjacent the notches havingsufficient free area for bonding with the elastomer of the teeth;

applying a tensile layer about the wear-resistant fabric;

introducing a substantially liquid elastomeric material into the moldcavity, whereby the liquid elastomeric material does not penetrate saidoutermost surface of the fabric layer;

polymerizing the thus formed product; and

removing the elastomer impervious material from the adjacentwear-resistant fabric whereby the outermost driving surface portion ofthe fabric layer exposed is free of the cast elastomer.

9. The method of claim 8 wherein the elastomer impervious material isbonded to the wear-resistant fabric so that the elastomer imperviousmaterial penetrates no more than 60% of the depth of the fabric layer.

10. The method of claim 8 wherein the wear-resistant fabric is made of afibrous layer, the fibers along said outermost driving portion beingfree from total encapsulation by the elastomer in the finished belt.

1 1. The method of claim 8 wherein the elastomer impervious material haspoor abrasion resistance, and including the further step of operatingsaid belt in a cooperating sprocket drive so as to at least partiallywear off said polymer impervious material from the belt.

12. The method of claim 8 wherein the polymer impervious material isformed of a polymeric sheet which has significantly lower coefficient offriction than the elastomeric material of the belt.

13. A method for producing a liquid cast polyurethane positive drivepower transmission belt having a polyurethane body, a tensile sectiondisposed within said body, and a series of polyurethane-containing teethintegral with the body and positioned along the inner peripheral surfaceof the belt and having an outer fabric surface bonded to the teeth, theoutermost driving surface portion of which is substantially free ofurethane, comprising the steps of:

bonding to one side of the wear-resistant fabric a layer of polyurethaneimpervious material, the layer of polyurethane impervious material beingcomposed of a material other than polyurethane and penetrating into andsealing said outermost surface of the fabric layer, with the depth ofpenetration of the polyurethane impervious material being no more thanabout 60% of the thickness of the wear-resistant fabric; forming a moldcavity between a notched mold man drel and an outer shell, said notchescorresponding to the teeth to be formed in the positive drive belt;

wrapping the bonded wear-resistant fabric about the notched mold mandrelin a manner such that the layer of polyurethane impervious material ismade to substantially conform to the notches in the mold, the side ofthe wear-resistant fabric opposite the notches having sufficient freearea to bond to the urethane of the belt;

applying a tensile layer;

introducing a substantially liquid polyurethane material into the moldcavity, whereby the urethane impervious material prevents the liquidurethane introduced into the mold from penetrating said outermostsurface of the fabric layer adjacent the notched mold portion;

polymerizing the thus formed product to produce a sleeve of belting fromwhich one or more positive drive endless belts may be made.

14. The method of claim 13 wherein the depth of penetration of theurethane impervious material into the wear-resistant fabric layer is nomore than about 20%.

15. The method of claim 13 wherein the depth of penetration of theurethane impervious material into the wear-resistant fabric layer is inthe range from about 4 to about 8%.

16. The method of claim 13 wherein the urethane impervious material isformed of a polymeric sheeting which is made to be heat bonded to thewear-resistant fabric layer, said polymeric sheeting having acoefficient of friction less than the coefficient of friction of theurethane.

17. The method of claim 13 wherein the urethane impervious material hasgood abrasion resistance and a coefficient of friction which issignificantly lower than the coefficient of friction of the urethane.

18. A method for the production of positive drive liquid castableelastomeric power transmission belts including a plurality of teethloaded with the cast elastomer and disposed along the driving surface ofthe belt, the teeth carrying on their outer surface a wearresistantfabric layer the outermost driving surface portion of which issubstantially free of said cast elastomer, comprising the steps of:

attaching to at least one side of the wear-resistant fabric a layer ofpolymeric thermoplastic material which is impervious to the liquidcastable elastomer, the layer of thermoplastic material penetrating intoand sealing said outermost surface of the fabric layer, the depth ofpenetration of the thermoplastic material into the fabric layer being atleast 4 percent, and said thermoplastic material being a materialdistinct from the cast elastomer;

forming a mold cavity between a mandrel and an outer shell, one of saidmandrel or shell having a plurality of notches;

disposing the wear-resistant fabric with the attached thermoplasticmaterial within the cavity in a manner such that the layer ofthermoplastic material is adjacent the notches, the side of thewear-resistant fabric opposite the side adjacent the notches havingsufficient free area for bonding with the elastomer of the teeth;

applying a tensile band about the wearresistant fabric',

introducing a substantially liquid elastomeric material into the moldcavity, whereby the liquid elastomeric material does not penetrate saidoutermost surface of the fabric layer; and

polymerizing the thus formed product.

1. IN A METHOD FOR PRODUCING A POSITIVE DRIVE CASTABLE ELASTOMERIC POWERTRANSMISSION BELT HAVING A PLURALITY OF SPACED COGS ATTACHED TO A BODYSECTION INCLUDING A TENSILE SECTION, SAID COGS HAVING POSITIONEDAPPROXIMATELY ALONG THEIR SURFACE A LAYER OF WEAR-RESISTANT FABRIC, THEIMPROVEMENT COMPRISING ISOLATING THE CAST ELASTOMER FROM THE OUTERSURFACE OF THE FABRIC LAYER BY THE STEPS OF: ADHERING TO ONE SIDE OF THEWEAR-RESISTANT FABRIC A LAYER OF ELASTOMER IMPERVIOUS MATERIAL WHICH HASBEEN CURED OR SET, THE LAYER OF ELASTOMER IMPERVIOUS MATERIALPENETRATING INTO AND SEALING SAID OUTER SURFACE OF THE FABRIC LAYER,SAID ELASTOMER IMPERVIOUS MATERIAL BEING A MATERIAL OF THE SAMD TYPE ORDIFFERENT TYPE FROM THE CAST ELASTOMER, FORMING A MOLD CAVITY DEFINED BYA MOLD MANDREL AND AN OUTER SHELL, ONE OF SAID MANDREL OR SHELL HAVING APLURALITY OF NOTCHES CORRESPONDING TO THE SHAPE OF THE COG, WRAPPING THEBONDED WEAR-RESISTANT FABRIC ABOUT THE SURFACE OF THE NOTCHED MOLDPORTION IN A MANNER SUCH THAT THE LAYER OF ELASTOMER IMPERVIOUS MATERIALIS ADJACENT THE NOTCHED MOLD PORTION, APPLYING A TENSILE LAYER ABOUT THEWEAR-RESISTANT FABRIC, AND INTRODUCING A SUBSTANTIALLY LIQUIDELASTOMERIC MATERIAL INTO THE MOLD CAVITY AND POLEMERIZING THE THUSFORMED PRODUCT, WHEREBY THE LIQUID ELASTOMERIC MATERIAL DOES NOTPENETRATE THE OUTER SURFACE OF THE FABRIC LAYER.
 2. The method of claim1 wherein the elastomer impervious material consists of a thin polymericsheet.
 3. The method of claim 2 wherein polyethylene sheet is heatbonded to one side only of the wear-resistant fabric at a temperatureand pressure so that the polyethylene penetrates through the surface onthe bonding side of the wear-resistant fabric, but does not penetratethe opposite surface of the wear-resistant fabric.
 4. The method ofclaim 3 wherein the temperature is maintained in the range from about230* to about 250*F.
 5. The method of claim 1 wherein the layer ofelastomer impervious material is brought adjacent the notched moldportion by the use of fibrous cross cords which are wound about thenotches of the mandrel and which are forced against the wear-resistantfabric by winding the tensile layer on top of such fibrous cross cordsurging the wear-resistant fabric into the notches.
 6. The method ofclaim 1 wherein the elastomer impervious material has poor abrasionresistance whereupon rotation of the belt about a cooperating sheavewill cause the elastomer impervious material to at least partially wearoff.
 7. The method of claim 1 wherein the layer of elastomer imperviousmaterial forms a strong bond with the cast elastomer and further whereinthe depth of penetration of the elastomer impervious material into thewear-resistant fabric layer is substantially 100 percent.
 8. A METHODFOR THE PRODUCTION OF POSITIVE DRIVE LIQUID CASTABLE ELASTOMERIC POWERTRANSMISSION BELTS INCLUDING A PLURALITY OF TEETH LOADED WITH THE CASTELASTOMER AND DISPOSED ALONG THE DRIVE SURFACE OF THE BELT, THE TEETHCARRYING ON THEIR OUTER SURFACE A WEAR-RESISTANT FABRIC LAYER THEOUTERMOST DRIVING SURFACE PORTION OF WHICH IS SUBSTANTIALLY FREE OF SAIDCAST ELASTOMER, COMPRISING THE STEPS OF: ATTACHING TO AT LEAST ONE SIDEOF THE WEAR-RESISTANT FABRIC A LAYER OF MATERIAL IMPERVIOUS TO THELIQUID CASTABLE ELASTOMER, THE LAYER OF IMPERVIOUS MATERIAL PENETRATINGINTO AND SEALING SAID OUTERMOST SURFACE OF THE FABRIC LAYER, FORMING AMOLD CAVITY BETWEEN A MANDREL AND AN OUTER SHELL, ONE OF SAID MANDREL ORSHELL HAVING A PLURALITY OF NOTCHES, DISPOSING THE WEAR-RESISTANT FABRICWITH THE ATTACHED ELASTOMER IMPERVIOUS MATERIAL WITHIN THE CAVITY IN AMANNER SUCH THAT THE LAYER OF ELASTOMER IMPERVIOUS MATERIAL IS ADJACENTTHE NOTCHES, THE SIDE OF THE WEAR-RESISTANT FABRIC OPPOSITE THE SIDEADJACENT THE NOTCHES HAVING SUFFICIENT FREE AREA FOR BONDING WITH THEELASTOMER OF THE TEETH, APPLYING A TENSILE LAYER ABOUT THEWEAR-RESISTANT FABRIC, INTRODUCING A SUBSTANTIALLY LIQUID ELASTOMERICMATERIAL INTO THE MOLD CAVITY, WHEREBY THE LIQUID ELASTOMERIC MATERIALDOES NOT PENETRATE SAID OUTERMOST SURFACE OF THE FABRIC LAYER,POLYMERIZING THE THUS FORMED PRODUCT, AND REMOVING THE ELASTOMERIMPERVIOUS MATERIAL FROM THE ADJACENT WEAR-RESISTANT FABRIC WHEREBY THEOUTERMOST DRIVING SURFACE PORTION OF THE FABRIC LAYER EXPOSED IS FREE OFTHE CAST ELASTOMER.
 9. The method of claim 8 wherein the elastomerimpervious material is bonded to the wear-resistant fabric so that theelastomer impervious material penetrates no more than 60% of the depthof the fabric layer.
 10. The method of claim 8 wherein thewear-resistant fabric is made of a fibrous layer, the fibers along saidoutermost driving portion being free from total encapsulation by theelastomer in the finished belt.
 11. The method of claim 8 wherein theelastomer impervious material has poor abrasion resistance, andincluding the further step of operating said belt in a cooperatingsprocket drive so as to at least partially wear off said polymerimpervious material from the belt.
 12. The method of claim 8 wherein thepolymer impervious material is formed of a polymeric sheet which hassignificantly lower coefficient of friction than the elastomericmaterial of the belt.
 13. A method for producing a liquid castpolyurethane positive drive power transmission belt having apolyurethane body, a tensile section disposed within said body, and aseries of polyurethane-containing teeth integral with the body andpositioned along the inner peripheral surface of the belt and having anouter fabric surface bonded to the teeth, the outermost driving surfaceportion of which is substantially free of urethane, comprising the stepsof: bonding to one side of the wear-resistant fabric a layer ofpolyurethane impervious material, the layer of polyurethane imperviousmaterial being composed of a material other than polyurethane andpenetrating into and sealing said outermost surface of the fabric layer,with the depth of penetration of the polyurethane impervious materialbeing no more than about 60% of the thickness of the wear-resistantfabric; forming a mold cavity between a notched mold mandrel and anouter shell, said notches corresponding to the teeth to be formed in thepositive drive belt; wrapping the bonded wear-resistant fabric about thenotched mold mandrel in a manner such that the layer of polyurethaneimpervious material is made to substantially conform to the notches inthe mold, the side of the wear-resistant fabric opposite the notcheshaving sufficient free area to bond to the urethane of the belt;applying a tensile layer; introducing a substantially liquidpolyurethane material into the mold cavity, whereby the urethaneimpervious material prevents the liquid urethane introduced into themold from penetrating said outermost surface of the fabric layeradjacent the notched mold portion; polymerizing the thus formed productto produce a sleeve of belting from which one or more positive driveendless belts may be made.
 14. The method of claim 13 wherein the depthof penetration of the urethane impervious material into thewear-resistant fabric layer is no more than about 20%.
 15. The method ofclaim 13 wherein the depth of penetration of the urethane imperviousmaterial into the wear-resistant fabric layer is in the range from about4 to about 8%.
 16. The metHod of claim 13 wherein the urethaneimpervious material is formed of a polymeric sheeting which is made tobe heat bonded to the wear-resistant fabric layer, said polymericsheeting having a coefficient of friction less than the coefficient offriction of the urethane.
 17. The method of claim 13 wherein theurethane impervious material has good abrasion resistance and acoefficient of friction which is significantly lower than thecoefficient of friction of the urethane.
 18. A method for the productionof positive drive liquid castable elastomeric power transmission beltsincluding a plurality of teeth loaded with the cast elastomer anddisposed along the driving surface of the belt, the teeth carrying ontheir outer surface a wear-resistant fabric layer the outermost drivingsurface portion of which is substantially free of said cast elastomer,comprising the steps of: attaching to at least one side of thewear-resistant fabric a layer of polymeric thermoplastic material whichis impervious to the liquid castable elastomer, the layer ofthermoplastic material penetrating into and sealing said outermostsurface of the fabric layer, the depth of penetration of thethermoplastic material into the fabric layer being at least 4 percent,and said thermoplastic material being a material distinct from the castelastomer; forming a mold cavity between a mandrel and an outer shell,one of said mandrel or shell having a plurality of notches; disposingthe wear-resistant fabric with the attached thermoplastic materialwithin the cavity in a manner such that the layer of thermoplasticmaterial is adjacent the notches, the side of the wear-resistant fabricopposite the side adjacent the notches having sufficient free area forbonding with the elastomer of the teeth; applying a tensile band aboutthe wear-resistant fabric; introducing a substantially liquidelastomeric material into the mold cavity, whereby the liquidelastomeric material does not penetrate said outermost surface of thefabric layer; and polymerizing the thus formed product.